The present invention relates to adjustment of image quality in an image forming apparatus such as a copying apparatus, a page printer, etc.
In color copying apparatuses employing an electrophotographic process, toner images of primary colors of yellow (Y), magenta and cyan (C) are sequentially formed and are placed on each other so as to form a color copied image. In the known color copying apparatuses, density of the toner image of each color, i.e. state of development by the toner of each color is an important factor in determination of color reproducibility (image quality).
Therefore, in the known color copying apparatuses, an AIDC pattern (reference toner image for adjusting development density) for the toner of each color is produced on a photosensitive member at a predetermined timing such that densities of the AIDC patterns are detected by respective photoelectric type AIDC sensors. In response of the detection signals, setting values of corona charging quantity for the photosensitive member, amount of exposure for charge erasing, developing bias voltage, etc. are changed in image forming processes of respective colors at the time of copying such that image quality is adjusted.
However, in the known color copying apparatuses, since the AIDC patterns corresponding to the toners of Y, M and C, respectively are sequentially produced, a long period is required for adjusting image quality, thereby resulting in delay in start of copying. Furthermore, the known color copying apparatuses have such a drawback that although the AIDC patterns occupy a small area, the toners of the respective colors are consumed for producing the AIDC patterns.